Segment Reporting (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Segment Reporting Information [Line Items]
Product revenues	$ 257,921	$ 264,586
Type of Revenue [Extensible List]	us-gaap:ProductMember	us-gaap:ProductMember
Sales Revenue, Net | Geographic Concentration Risk
Segment Reporting Information [Line Items]
Total product revenues in percentage	100.00%	100.00%
United States
Segment Reporting Information [Line Items]
Product revenues	$ 118,454	$ 120,350
United States | Sales Revenue, Net | Geographic Concentration Risk
Segment Reporting Information [Line Items]
Total product revenues in percentage	46.00%	46.00%
Germany
Segment Reporting Information [Line Items]
Product revenues	$ 23,210	$ 22,362
Germany | Sales Revenue, Net | Geographic Concentration Risk
Segment Reporting Information [Line Items]
Total product revenues in percentage	9.00%	8.00%
Japan
Segment Reporting Information [Line Items]
Product revenues	$ 18,591	$ 13,573
Japan | Sales Revenue, Net | Geographic Concentration Risk
Segment Reporting Information [Line Items]
Total product revenues in percentage	7.00%	5.00%
China
Segment Reporting Information [Line Items]
Product revenues	$ 15,597	$ 24,204
China | Sales Revenue, Net | Geographic Concentration Risk
Segment Reporting Information [Line Items]
Total product revenues in percentage	6.00%	9.00%
South Korea
Segment Reporting Information [Line Items]
Product revenues	$ 14,978	$ 13,822
South Korea | Sales Revenue, Net | Geographic Concentration Risk
Segment Reporting Information [Line Items]
Total product revenues in percentage	6.00%	5.00%
Czech Republic
Segment Reporting Information [Line Items]
Product revenues	$ 12,142	$ 11,715
Czech Republic | Sales Revenue, Net | Geographic Concentration Risk
Segment Reporting Information [Line Items]
Total product revenues in percentage	5.00%	5.00%
Canada
Segment Reporting Information [Line Items]
Product revenues	$ 10,291	$ 13,113
Canada | Sales Revenue, Net | Geographic Concentration Risk
Segment Reporting Information [Line Items]
Total product revenues in percentage	4.00%	5.00%
United Kingdom
Segment Reporting Information [Line Items]
Product revenues	$ 8,832	$ 10,845
United Kingdom | Sales Revenue, Net | Geographic Concentration Risk
Segment Reporting Information [Line Items]
Total product revenues in percentage	3.00%	4.00%
Romania
Segment Reporting Information [Line Items]
Product revenues	$ 6,922	$ 6,298
Romania | Sales Revenue, Net | Geographic Concentration Risk
Segment Reporting Information [Line Items]
Total product revenues in percentage	3.00%	2.00%
Other
Segment Reporting Information [Line Items]
Product revenues	$ 28,904	$ 28,304
Other | Sales Revenue, Net | Geographic Concentration Risk
Segment Reporting Information [Line Items]
Total product revenues in percentage	11.00%	11.00%
Non U.S.
Segment Reporting Information [Line Items]
Product revenues	$ 139,467	$ 144,236
Non U.S. | Sales Revenue, Net | Geographic Concentration Risk
Segment Reporting Information [Line Items]
Total product revenues in percentage	54.00%	54.00%